The present invention relates generally to the fabrication of a semiconductor device and more particularly to a system and a method for controlling processing of a moving substrate using scatterometry.
In the semiconductor industry, performance of components, such as, for example, transistors that are fabricated in an integrated circuit, strongly depend on the precision of manufacturing small features which form the transistor and also the application of various physical parameters during processing. For example, a variability in thickness of a thin film such as a gate dielectric can lead to variations in drive current of a transistor. Drive current, the current from source to drain of a transistor, is indicative of the speed performance of the transistor. A uniform drive current in transistors across a semiconductor wafer results in a uniform speed of transistors across the wafer and a low leakage current even in conditions when the drive current is high. On the other hand, a drive current that is non-uniform across a wafer may result in a high standby current, a high leakage current and high power consumption by the integrated circuit. Drive current uniformity is sought by reducing the variability in parameters, such as gate dielectric thin film thickness, which give rise to drive current variations.
Conditions affecting the thin film thickness on a substrate being processed in a process chamber can vary in an uncontrolled manner from batch to batch, thereby causing inconsistent results. Variations in temperature, pressure, gas flow rate, and gas composition, for example, utilized in the thin film formation process can lead to significant variations in thin film thickness. A non-uniform thin film thickness resulting in a non-uniform drive current for a transistor can have a significant impact upon the quality of a resulting integrated circuit formed on the substrate.
Obtaining precision control of the thin film formation process is one challenging aspect of forming a thin film on a substrate. Prior art techniques for measuring thin film thickness on a substrate can be employed to obtain a higher degree of precision in controlling the formation of the thin film. For example, optical scattering techniques can be utilized to measure the thin film. U.S. Pat. No. 5,343,293 discloses an optical ellipsometer measurement device for measuring the thickness of oxide films on silicon wafers based upon a discernable change in polarized light passing through the film. Data obtained from the ellipsometer measurement can further be utilized to characterize the thin film formed on the substrate, and to further control the formation of the oxide film.
Some processes, however, employ a procedure wherein the substrate moves, typically in a rotational manner, within the process chamber. Rotating the substrate within the process chamber provides even exposure of the substrate to varying conditions within different regions of the process chamber, thereby increasing the thin film uniformity across the substrate. Prior art methods of utilizing optical scattering techniques are difficult to utilize on a moving substrate, however, due to the nature of measuring scattered light from a moving target.
Therefore, there remains an unsatisfied need for a system and a method that provides precise control of a formation of a thin film on a moving substrate using an optical scattering measurement technique.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its primary purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
The present invention generally relates to the fabrication of a semiconductor device and more particularly to a system and a method for controlling a thin film formation process. According to one exemplary aspect of the present invention, scatterometry is used as a tool to measure a thin film thickness on a moving substrate. Scatterometry permits in-situ measurements of thin film formation, whereby thin film formation process conditions are controlled in a feedback loop to obtain a targeted result. Scatterometry is facilitated, for example, by providing a grating pattern in a non-production region of a substrate. A signaling device is utilized to strobe the scatterometry measurement at a location on the moving substrate, whereby the substantially same location on the substrate is consistently measured.